Seven countries signed a treaty binding each of them to perform specified actions on a certain fixed date, with the actions of each conditional on simultaneous action taken by the other countries. Each country was also to notify the six other countries when it had completed its action.

The simultaneous-action provision of the treaty leaves open the possibility that

(A) the compliance date was subject to postponement, according to the terms of the treaty

(B) one of the countries might not be required to make any changes or take any steps in order to comply with the treaty, whereas all the other countries are so required.

(C) each country might have a well-founded excuse, based on the provision, for its own lack of compliance

(D) the treaty specified that the signal for one of the countries to initiate action was notification by the other countries that they had completed action

(E) there was ambiguity with respect to the date after which all actions contemplated in the treaty are to be complete.

这个题目答案是C让我百思不得其解。说几个国家同时做，但是做完后要告诉别人。这里和excuse没有什么关系呀。请nn指教一二。

The treaty mandates that each of the 6 countries must "perform specified actions on a certain fixed date, with the actions of each (country) conditional on simultaneous action taken by the other countries."

This arrangement leaves open the possibility that none of the countries will take action, and each will claim that the reason of its inaction is that other countries are not taking simultaneous actions. This is what C describes, therefore C is the best answer.